1. Field of the Invention
The present invention relates to a method of introducing an ion. Further, the present invention also relates to a method of manufacturing a semiconductor device which is manufactured by a step comprising introducing an ion. As used herein, the term “semiconductor device” is intended to include all devices which can exert functions thereof by making use of semiconductor characteristics. It is construed that the term “semiconductor device” is further intended to include in the category thereof other devices, such as a liquid crystal display device in which a thin film transistor and liquid crystal are combined with each other, and a light emitting device in which a thin film transistor and a light emitting element are combined with each other.
2. Description of the Related Art
A technique for manufacturing a circuit having a predetermined function by first forming an element such as a thin film transistor on a surface of a semiconductor and then connecting it by wiring has been well known. In this technique, an ion-introducing technique for forming an impurity region having a conductivity type of n type or p type in a predetermined region has become essential.
As the ion-introducing technique, a technique in which a plurality of ions which differ in mass from one another are generated by converting a material gas into a plasma state by a trigger electrode and, then, the thus-generated ions in the plasma are imparted with an appropriate energy by a drawing electrode system or an acceleration electrode system arranged in a chamber and, thereafter, the ions thus imparted with the energy are introduced into a semiconductor has been known. Further, there is a case in which, after the material gas is changed into a plasma state to generate ions, only ions selected thereamong by a mass separation method are introduced in the semiconductor. Characteristics of the ion-introducing technique are in that it is possible to implant an impurity element having a predetermined concentration into a predetermined depth in the semiconductor by controlling an acceleration voltage or an ion density. Examples of illustrative apparatuses to be adopted in this occasion include an ion-doping apparatus, and an ion-implanting apparatus.
Further, there is another case in which an ion is introduced only in a desired region in a semiconductor. For example, a resist comprising an organic film is partially formed on the semiconductor and, then, the ion is introduced while using the thus-formed resist as a mask to allow the ion to be introduced only in a region on which the resist is not formed.
However, when the resist is formed on the semiconductor, the ion is introduced also in the resist. Therefore, the ion imparted with energy is allowed to react with a component of the resist to generate a gas, which is herein referred to as a “dissociated gas”. Since the resist is ordinarily an organic film, components of the dissociated gas comprise nitrogen, carbon, oxygen, hydrogen, and water vapor. When the dissociated gas is generated, a component of the dissociated gas is implanted in the semiconductor together with the ion imparted with energy. FIG. 6 shows distributions of boron (B), carbon (C), oxygen (O) and nitrogen (N) in a silicon wafer at the time boron is introduced into each of the silicon wafer on which a resist is formed (shown in a heavy line) and the silicon wafer on which the resist is not formed (shown in a thin line). The ion was introduced under the following conditions: a material gas was B2H6; a radio frequency supply was 20 W; an acceleration voltage was 65 kV; and a dose rate was 3.3×1015 atoms/cm2. It can be seen from FIG. 6 that carbon (C), oxygen (O), and nitrogen (N) are distributed in a greater extent in the silicon wafer on which the resist is formed than in the silicon wafer on which the resist is not formed. In order to enhance properties of the semiconductor, it is desirable to allow such distributions to be smaller by even a small extent.
Further, since the resist is partially formed on the semiconductor, the dissociated gas is locally generated to cause a quantity of ion to be introduced in the semiconductor to be unevenly distributed. Furthermore, since pressure inside a treatment chamber in which the introduction of the ion is performed varies due to the generation of the dissociated gas, arcing may sometimes appear, or an ion density or an acceleration voltage is adversely affected to allow the ion introduction conditions to depart from the set ion introduction conditions. This is a serious problem in a recent trend in which a size of a substrate is being enlarged and also becomes a major factor of deteriorating semiconductor properties.
Then, as a method for decreasing the generation of the dissociated gas, there is a method of performing baking processing or a UV irradiation before the ion is introduced. By this method, the resist is cured to thereby decrease the generation of the dissociated gas. On the other hand, since the resist is employed merely as a mask for the purpose of allowing the ion to be introduced only in a desired region, it is necessary to remove the resist after the ion is introduced. However, it is sometimes difficult to completely remove the resist which has been cured by the baking processing or the UV irradiation even with ashing, peeling, or other appropriate processing. Since the resist is ordinarily an organic film, when the resist remains on the semiconductor as a residue, an apparatus to be used in a subsequent step in the introduction of the ion is contaminated whereupon such contamination will cause deterioration of not only properties of the semiconductor of interest but also properties of other semiconductors and will, then, give a detrimental effect on operating characteristics of the semiconductor device. Further, such contamination will deteriorate a coating property of a film to be formed after the ion is introduced whereupon such deterioration may cause a malfunction such as wire breakage. Furthermore, performing the baking processing or the UV irradiation increases a number of processing steps to thereby cause an increase of an overall processing time or cost.